Epac2 Mediates Cardiac (cid:533) 1 -Adrenergic Dependent SR Ca 2+ Leak and Arrhythmia

: Background — (cid:533) -adrenergic receptor ( (cid:533) -AR) activation can provoke cardiac arrhythmias mediated by cAMP-dependent alterations of Ca 2+ signaling. However cAMP can activate both PKA and an Exchange protein directly activated by cAMP ( Epac ) but their functional interaction is unclear. In heart selective Epac activation can induce potentially arrhythmogenic sarcoplasmic reticulum (SR) Ca 2+ release that involves CaMKII effects on the ryanodine receptor (RyR). Methods and Results — We tested whether physiological (cid:533) -AR activation causes Epac-mediated SR Ca 2+ leak and arrhythmias, whether it requires Epac1 vs. Epac2, (cid:533) 1 -AR vs. (cid:533) 2 -AR and CaMKII (cid:303) -dependent phosphorylation of RyR2-S2814. We used knockout mice for Epac1, Epac2 or both (DKO). All knockouts exhibited unaltered basal cardiac function, Ca 2+ handling and hypertrophy in response to pressure overload. However, SR Ca 2+ leak induced by the specific Epac activator 8-CPT in wild-type was abolished in Epac2-KO and DKO, but unaltered in Epac1-KO. (cid:533) -AR-induced arrhythmias were also less inducible in Epac2-KO vs. wild-type. (cid:533) AR activation with PKA inhibition, mimicked 8-CPT effects on SR Ca 2+ leak, and was prevented by blockade of (cid:533) 1 -AR but not (cid:533) 2 -AR. CaMKII inhibition (KN93) and genetic ablation of either CaMKII (cid:303) or CaMKII phosphorylation on RyR2-S2814 prevented 8-CPT-induced SR Ca 2+ leak. phosphorylation of RyR2-S2814. This pathway contributes to (cid:533) -AR-induced arrhythmias and reduced cardiac function. phosphomimetic RyR2-S2814D mice. In conclusion, our work indicates that (cid:533) (cid:1187) -AR activates Epac2-dependent SR Ca 2+ leak and arrhythmia via CaMKII (cid:303) -dependent phosphorylation of RyR2-S2814. These findings give new insights into Epac physiology and pathology. Indeed, Epac seems non-essential for baseline cardiac function, and does not significantly attenuate the acute inotropic response to potent (cid:533) -AR activation or the early hypertrophic response to pressure overload. However, we demonstrate a specific role for the Epac2 isoform in mediating PKA-independent SR Ca 2+ leak via (cid:533) (cid:1187) -AR causing RyR-S2814 phosphorylation by CaMKII (cid:303) and SR Ca 2+ leak. Further investigations understand why both Epac and PKA are activated by (cid:533) 1 -AR stimulation and the role of Epac1 (nuclear signaling vs. RyR function or transition to HF). isissolololatatatededed rrratatat